The disclosed invention deals in the art of security validation apparatus and particularly improvements therein. In the known art, devices exist whereby the validation of currency, securities and the like may be achieved by masking certain areas of the instrument with a reticle or other suitable element to determine the presence or absence of a particular pattern thereon. However, with increased sophistication of photocopying apparatus, high resolution copies of such instruments may be obtained which can pass these pattern matching primary tests and cause the validation apparatus to accept photocopies as true and valid instruments. Consequently, it has become desirable to develop apparatus for conducting secondary tests for security validation to detect and reject such photocopies and other facsimiles.
The so-called single-sided photocopies of a valid instrument may be readily detected by capitalizing on the discovered fact that most securities are two-sided and, on the side opposite that bearing the pattern tested with the primary test, there generally exists two areas, either adjacent or otherwise; one of a highly light reflective nature and the other of a lower light reflective nature. A ratio exists between the two. It has been demonstrated that on a given instrument the ratio of reflectances of the two areas is consistent among like instruments. This is primarily a result of the printing and process control involved in the manufacture of the instrument. Furthermore, it has been demonstrated that percent reflectance from either area with respect to an energy bandwidth is predictable within a certain tolerance. Consequently, a relationship exists between the emitted light and the reflected light from an area of an instrument. On a single-sided photocopy, such areas will obviously not be present and hence a test of the relative reflective characteristics of these areas will fail. While some instruments do not have two distinct neighboring areas, a reflectory may be used to simulate one area. This technique generally would be used against the single-sided copy but it can be extended to be used to discriminate against the bottom side of a double-sided copy.
With the advent of the production of double-sided photocopies, it has been found that the above-recited tests for relative reflective characteristics may be utilized to distinquish between the legitimate instrument and the double-sided copy. The technique may be applied to either side of the instrument. The light reflective characteristics may be tested by using an infrared light and testing a first area on the instrument which has a low reflectance as to infrared and a second area which is highly reflective with respect thereto. The tests may also operate in the visible range and test areas of the instrument of different colors, such areas being reflective as to light of the color of the area and absorptive with respect to other such light. In this type system, a bandwidth of usable light falls on the two areas. One area reflects a high percentage of the light and the other a low percentage. By relying on the fact that photocopies generally reproduce with ink or toner which is absorptive as to infrared as well as color and only in black and white (not color), this reflective ratio test may be conducted inasmuch as the relative reflective characteristics of the instrument are nonexistent in a photocopy. Further, even with a two-sided photocopy, tests may be utilized to compare the relative values of reflectance against a related reference to guarantee that not only the high to low reflection ratio exists, but also that such ratio is within a particular bandwidth, such criteria being difficult to reproduce via a photocopy.
It has also been found in security validation testing that the testing of an instrument against absolute values is not always accurate inasmuch as aging of the equipment, the gathering of dust and dirt on lenses, the shifting of filaments within lamps, and the age and condition of the instrument itself all have a bearing upon readings against absolute values. Consequently, it has been found that ratios or relative comparisons of one area of the note against another provide the most accurate means for testing validity without chancing an inordinate number of rejections of valid instruments.